The present invention relates to a global positioning system (GPS) receiver, and in particular to avoiding interference to a GPS receiver from wireless transmissions by time multiplexing the reception of a GPS signal.
The global positioning system (GPS) is based on an earth-orbiting constellation of twenty-four satellite vehicles each broadcasting its precise location and ranging information. From any location on or near the earth, a GPS receiver with an unobstructed view of the sky should be able to track at least four satellite vehicles, thereby being able to calculate the receiver""s precise latitude, longitude, and elevation. Each satellite vehicle constantly transmits two signals, generally referred to as L1 and L2. The L1 signal from a satellite vehicle contains a unique pseudo-random noise code ranging signal (C/A code) with a chipping frequency of 1.023 MHz, system data with a bitrate frequency of 50 Hz, and an encrypted precise-code (y-code) with a chipping frequency of 10.23 MHz all being modulated onto a carrier frequency of 1575.42 MHz. The L2 signal consists of the system data and y-code being modulated onto a carrier frequency of 1227.60 MHz.
In order to calculate a three-dimensional location, a receiver must determine the distance from itself to at least four satellite vehicles. This is accomplished by first determining the location of at least four satellite vehicles using ephemeris data received from the satellites. Once the locations of the satellites have been determined, the distance from the receiver to each of the satellites is calculated based upon the current estimate of receiver position. The measurement of the distance from the receiver to a satellite is based on the amount of time that elapsed between the transmission of a ranging signal from each satellite vehicle and the reception of that chip symbol by the receiver. In particular, the estimated position of the receiver is then corrected based upon a time epoch associated with the received ranging signal.
In many applications, it is desirable to avoid degradation of the GPS receiver due to a strong signal being transmitted from an associated wireless communications device. One such application is the incorporation of the GPS receiver into a mobile phone. Transmissions from the mobile phone, which are much stronger than the L1 or L2 signals, may interfere with the operation of the GPS receiver. Thus, there remains a need for a GPS receiver capable of operating efficiently when incorporated in a device having a wireless transmitter.
The jammer response circuitry of the present invention operates to control correlation circuitry in a GPS receiver based on an occurrence of a transmission from a wireless transmitter, thereby avoiding performance degradation in the GPS receiver due to interference caused by the transmission, In general, the jammer response circuitry activates a control signal during the transmission, thereby temporarily stopping the operation of the correlation circuitry. More particularly, the accumulation of results of a correlation of a received signal with a generated frequency and a generated code having numerous time offsets is temporarily stopped when the control signal is activated and resumes operation when the control signal is deactivated. In one embodiment, the jammer response circuitry may be part of a wireless communications device, such as a mobile phone. In another embodiment, the GPS receiver and the jammer response circuitry may be incorporated into a wireless communications device, such as a mobile phone.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.